Variable displacement vane pump

ABSTRACT

A variable displacement vane pump includes a drive shaft; a rotor formed with slots; vanes received by the slots; a cam ring which can become eccentric and cooperates with the rotor and vanes to define pump chambers; suction and discharge ports opened to the pump chambers; a sealing member dividing a space on an outer circumferential surface of the cam ring into first and second fluid pressure chambers; a metering orifice formed on a discharge passage connected with the discharge port; and a pressure control section adapted to control a pressure which is introduced into the first or second fluid pressure chamber. The pressure control section includes a high pressure chamber into which an upstream pressure of metering orifice is introduced, a medium pressure chamber into which a downstream pressure of metering orifice is introduced, and a low pressure chamber connected with a reservoir tank. The vane pump further includes a relief valve adapted to drain the downstream pressure of metering orifice to the reservoir tank; and a variable metering mechanism configured to narrow an area of the metering orifice at least when the relief valve is opened.

BACKGROUND OF THE INVENTION

The present invention relates to a variable displacement vane pump, moreparticularly to a variable displacement vane pump for a power steeringapparatus.

Japanese Patent Application Publication No. 2003-21076 discloses apreviously-proposed variable displacement vane pump. In this technique,the variable displacement vane pump includes a relief valve installedinside a control valve. This relief valve serves to release adischarge-side pressure into a reservoir tank when the discharge-sidepressure becomes higher than or equal to a predetermined pressure.

SUMMARY OF THE INVENTION

However, in the above technique, in the case of trying to enhance a fueleconomy by reducing a relief amount of working fluid from the reliefvalve by means of a narrowing of a pilot orifice, the relief valveitself is vibrated due to a vibration of working fluid caused when theworking fluid passes through the pilot orifice. If the relief amount isreduced by use of a damper orifice instead of the pilot orifice in orderto avoid this vibration, the working fluid leaks from an annular portionof the control valve.

Accordingly, a pressure difference of valve is reduced so that a controlflow rate under a high pressure state is increased. Thereby, a pumpworkload is increased so as to cancel out an effect of reducing the fuelconsumption which is obtained by the reduction of relief amount ofworking fluid. There has been such a problem.

It is therefore an object of the present invention to provide a variabledisplacement vane pump devised to reduce the relief amount and tosuppress the increase in pump workload so as to enhance the fueleconomy.

According to one aspect of the present invention, there is provided avariable displacement vane pump comprising: a pump body; a drive shaftsupported rotatably by the pump body; a rotor disposed inside the pumpbody and adapted to be rotatably driven by the drive shaft, the rotorbeing formed with a plurality of slots spaced from each other in acircumferential direction of the rotor; a plurality of vanes received bythe slots so as to be movable out from the slots and into the slots; acam ring formed in an annular shape and disposed inside the pump body topermit the cam ring to become eccentric relative to the drive shaft, thecam ring cooperating with the rotor and the vanes to define a pluralityof pump chambers on an inner circumferential side of the cam ring; afirst plate member and a second plate member disposed on axially bothsides of the cam ring; a suction port provided on a side of at least oneof the first plate member and the second plate member and opened to atleast one of the plurality of pump chambers; a discharge port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; asealing member provided on an outer circumferential side of the camring, the sealing member dividing a space on an outer circumferentialsurface of the cam ring into a first fluid pressure chamber and a secondfluid pressure chamber, wherein a flow rate of working fluid dischargedfrom the discharge port is increased when the cam ring moves to thefirst fluid pressure chamber, wherein the flow rate of working fluiddischarged from the discharge port is decreased when the cam ring movesto the second fluid pressure chamber; a metering orifice formed on adischarge passage connected with the discharge port; a pressure controlsection adapted to control a pressure which is introduced into the firstfluid pressure chamber or the second fluid pressure chamber, thepressure control section comprising a high pressure chamber into whichan upstream pressure of the metering orifice is introduced, a mediumpressure chamber into which a downstream pressure of the meteringorifice is introduced, and a low pressure chamber connected with areservoir tank for storing working fluid; a relief valve providedbetween a downstream side of the metering orifice and the reservoirtank, the relief valve being adapted to be opened by receiving apressure greater than or equal to a predetermined level and thereby todrain the downstream pressure of the metering orifice to the reservoirtank; and a variable metering mechanism configured to narrow across-sectional area of opening portion of the metering orifice at leastwhen the relief valve is opened.

According to another aspect of the present invention, there is provideda variable displacement vane pump comprising: a pump body; a drive shaftsupported rotatably by the pump body; a rotor disposed inside the pumpbody and adapted to be rotatably driven by the drive shaft, the rotorbeing formed with a plurality of slots spaced from each other in acircumferential direction of the rotor; a plurality of vanes received bythe slots so as to be movable out from the slots and into the slots; acam ring formed in an annular shape and disposed inside the pump body topermit the cam ring to become eccentric relative to the drive shaft, thecam ring cooperating with the rotor and the vanes to define a pluralityof pump chambers on an inner circumferential side of the cam ring; afirst plate member and a second plate member disposed on axially bothsides of the cam ring; a suction port provided on a side of at least oneof the first plate member and the second plate member and opened to atleast one of the plurality of pump chambers; a discharge port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; asealing member provided on an outer circumferential side of the camring, the sealing member dividing a space on an outer circumferentialsurface of the cam ring into a first fluid pressure chamber and a secondfluid pressure chamber, wherein a flow rate of working fluid dischargedfrom the discharge port is increased when the cam ring moves to thefirst fluid pressure chamber, wherein the flow rate of working fluiddischarged from the discharge port is decreased when the cam ring movesto the second fluid pressure chamber; a metering orifice formed on adischarge passage connected with the discharge port; a pressure controlsection adapted to control a pressure which is introduced into the firstfluid pressure chamber or the second fluid pressure chamber, thepressure control section comprising a high pressure chamber into whichan upstream pressure of the metering orifice is introduced, a mediumpressure chamber into which a downstream pressure of the meteringorifice is introduced, and a low pressure chamber connected with areservoir tank for storing working fluid; a relief valve providedbetween a downstream side of the metering orifice and the reservoirtank, the relief valve being adapted to be opened by receiving apressure greater than or equal to a predetermined level and thereby todrain the downstream pressure of the metering orifice into the reservoirtank; and a variable metering mechanism configured to narrow across-sectional area of opening portion of the metering orifice when adischarge pressure on a downstream side of the discharge port is higherthan or equal to a predetermined pressure.

According to still another aspect of the present invention, there isprovided a variable displacement vane pump comprising: a pump body; adrive shaft supported rotatably by the pump body; a rotor disposedinside the pump body and adapted to be rotatably driven by the driveshaft, the rotor being formed with a plurality of slots spaced from eachother in a circumferential direction of the rotor; a plurality of vanesreceived by the slots so as to be movable out from the slots and intothe slots; a cam ring formed in an annular shape and disposed inside thepump body to permit the cam ring to become eccentric relative to thedrive shaft, the cam ring cooperating with the rotor and the vanes todefine a plurality of pump chambers on an inner circumferential side ofthe cam ring; a first plate member and a second plate member disposed onaxially both sides of the cam ring; a suction port provided on a side ofat least one of the first plate member and the second plate member andopened to at least one of the plurality of pump chambers; a dischargeport provided on a side of at least one of the first plate member andthe second plate member and opened to at least one of the plurality ofpump chambers; a sealing member provided on an outer circumferentialside of the cam ring, the sealing member dividing a space on an outercircumferential surface of the cam ring into a first fluid pressurechamber and a second fluid pressure chamber, wherein a flow rate ofworking fluid discharged from the discharge port is increased when thecam ring moves to the first fluid pressure chamber, wherein the flowrate of working fluid discharged from the discharge port is decreasedwhen the cam ring moves to the second fluid pressure chamber; a meteringorifice formed on a discharge passage connected with the discharge port;a pressure control section adapted to control a pressure which isintroduced into the first fluid pressure chamber or the second fluidpressure chamber, the pressure control section comprising a highpressure chamber into which an upstream pressure of the metering orificeis introduced, a medium pressure chamber into which a downstreampressure of the metering orifice is introduced, and a low pressurechamber connected with a reservoir tank for storing working fluid; arelief valve provided between a downstream side of the metering orificeand the reservoir tank, the relief valve being adapted to be opened byreceiving a pressure greater than or equal to a predetermined level andthereby to drain the downstream pressure of the metering orifice intothe reservoir tank; and a variable metering mechanism configured tonarrow a cross-sectional area of opening portion of the metering orificeto a larger extent as the eccentricity of the cam ring becomes smallerwhen the relief valve is open.

According to still another aspect of the present invention, there isprovided a variable displacement vane pump comprising: a pump body; adrive shaft supported rotatably by the pump body; a rotor disposedinside the pump body and adapted to be rotatably driven by the driveshaft, the rotor being formed with a plurality of slots spaced from eachother in a circumferential direction of the rotor; a plurality of vanesreceived by the slots so as to be movable out from the slots and intothe slots; a cam ring formed in an annular shape and disposed inside thepump body to permit the cam ring to become eccentric relative to thedrive shaft, the cam ring cooperating with the rotor and the vanes todefine a plurality of pump chambers on an inner circumferential side ofthe cam ring; a first plate member and a second plate member disposed onaxially both sides of the cam ring; a suction port provided on a side ofat least one of the first plate member and the second plate member andopened to at least one of the plurality of pump chambers; a dischargeport provided on a side of at least one of the first plate member andthe second plate member and opened to at least one of the plurality ofpump chambers; a sealing member provided on an outer circumferentialside of the cam ring, the sealing member dividing a space on an outercircumferential surface of the cam ring into a first fluid pressurechamber and a second fluid pressure chamber, wherein a flow rate ofworking fluid discharged from the discharge port is increased when thecam ring moves to the first fluid pressure chamber, wherein the flowrate of working fluid discharged from the discharge port is decreasedwhen the cam ring moves to the second fluid pressure chamber; a meteringorifice formed on a discharge passage connected with the discharge port;a pressure control section adapted to control a pressure which isintroduced into the first fluid pressure chamber or the second fluidpressure chamber, the pressure control section comprising a highpressure chamber into which an upstream pressure of the metering orificeis introduced, a medium pressure chamber into which a downstreampressure of the metering orifice is introduced, and a low pressurechamber connected with a reservoir tank for storing working fluid; afluid-pressure sensor adapted to sense a pressure discharged from thedischarge port; a relief valve adapted to drain the downstream pressureof the metering orifice to the reservoir tank, and a pressure-usingdevice adapted to use a pressure supplied from the discharge port; and avariable metering mechanism configured to narrow a cross-sectional areaof flow passage of the metering orifice on the basis of an output signalof the fluid-pressure sensor.

The other objects and features of this invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a vane pump in a first embodimentaccording to the present invention, taken in an axial direction of thevane pump.

FIG. 2 is a cross-sectional view of the vane pump in the firstembodiment, taken in a radial direction of the vane pump (at maximumswing position).

FIG. 3 is an enlarged cross-sectional view near a variable meteringmechanism.

FIG. 4 is a view showing the relation between an opening area ofmetering orifice and a swing amount of cam ring.

FIG. 5 is a view showing an example in which a minimum secured area ofthe metering orifice is provided as a separate hole.

FIG. 6 is an enlarged view of FIG. 5.

FIG. 7 is a view showing an example in which the metering orifice isprovided as a plurality of round holes.

FIG. 8 is a view showing an example in which a damper orifice isprovided outside a first housing.

FIG. 9 is a view showing an example in which a piston adapted to move inand out in response to the swing of cam ring is formed with the meteringorifice.

FIG. 10 is a cross-sectional view of a vane pump in a second embodimentaccording to the present invention, taken in an axial direction of thevane pump.

FIG. 11 is a cross-sectional view of the vane pump in the secondembodiment, taken in a radial direction of the vane pump.

FIG. 12 is a view showing an example in which a spool is provided as anelectromagnetic valve in the second embodiment.

FIG. 13 is a view showing an example in which a relief valve is providedoutside a housing in the second embodiment.

FIG. 14 is a view showing an example in which a shape of the spool ischanged in a manner that the spool is operated by use of a drainpressure produced at a downstream side of the relief valve in the secondembodiment.

FIG. 15 is an enlarged view of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

Reference will hereinafter be made to the drawings in order tofacilitate a better understanding of the present invention. Variabledisplacement vane pumps according to the present invention will beexplained below based on embodiments of the present invention, referringto the drawings.

First Embodiment

[Overview Structure of Vane Pump]

A first embodiment according to the present invention will now beexplained. FIG. 1 is a cross-sectional view of a vane pump 1 in thefirst embodiment, taken in an axial direction of the vane pump 1. FIG. 2is a cross-sectional view of the vane pump 1, taken in a radialdirection of the vane pump 1. FIG. 2 shows the state where a cam ring 4has moved to its most negative position relative to y-axis (maximumeccentricity amount). In FIG. 2, Oc denotes a center of the cam ring 4,and O_(R) denotes a center of a drive shaft 2.

X-axis is defined as the axial direction of the drive shaft 2, and apositive direction of x-axis is defined as a direction in which thedrive shaft 2 is inserted into first and second housings 11 and 12.Moreover, y-axis is defined as an axial direction of a spring 91 (seeFIG. 2) for regulating a swing (oscillation) of the cam ring 4. Anegative direction of y-axis is defined as a direction in which thespring 91 biases or urges the cam ring 4. Z-axis is defined as an axisorthogonal to x-axis and y-axis, and a positive direction of z-axis isdefined as a direction toward an inlet port IN.

The vane pump 1 includes the drive shaft 2, a rotor 3, the cam ring 4,an adapter ring 5 and a pump body 10. The drive shaft 2 is connectedthrough a pulley with an engine. The drive shaft 2 is supportedrotatably by the pump body 10, and rotates integrally with the rotor 3.

An outer circumferential portion of the rotor 3 is formed with aplurality of slots 31 as axial grooves. The plurality of slots 31 aregiven radially in the rotor 3, and are spaced from each other in thecircumferential direction of rotor 3. A vane 32 is inserted into orreceived by each slot 31 to allow the vane 32 to rise and fall in theradial direction of rotor 3. That is, each vane 32 can move in theoutward and inward directions of the slot 31. Each slot 31 iscontinuously connected with a back pressure chamber 33 which is providedat a radially-inner end of the slot 31 and which is supplied with afluid pressure. This fluid pressure biases or urges the vane 32outwardly in the radial direction.

The pump body 10 includes a first housing 11 and a second housing 12(corresponding to a first plate member according to the presentinvention). The first housing 11 is shaped like a cup having its bottom(11 a) and is opening in the positive direction of x-axis. A pressureplate 6 (corresponding to a second plate member according to the presentinvention) in the form of a circular disc is disposed on the bottomportion 11 a of first housing 11. That is, the first housing 11accommodates the pressure plate 6 on the bottom portion 11 a. The firsthousing 11 includes a pump element receiving portion 11 b at an innercircumferential portion of first housing 11. The pump element receivingportion 11 b accommodates or receives the adapter ring 5, cam ring 4 androtor 3 which are located adjacent to the pressure plate 6 in thepositive direction of x-axis.

The second housing 12 fluid-tightly abuts on the adapter ring 5, camring 4 and rotor 3 from the positive side of x-axis. The adapter ring 5,cam ring 4 and rotor 3 are supported by the pressure plate 6 and thesecond housing 12 so as to be sandwiched between the pressure plate 6and the second housing 12.

A suction port 62 and a discharge port 63 are provided in an x-axispositive side surface 61 of the pressure plate 6. Similarly, a suctionport 121 and a discharge port 122 are provided in an x-axis negativeside surface 120 of the second housing 12. The suction ports 62 and 121are connected with the inlet port IN. The discharge ports 63 and 122 areconnected with an outlet port OUT. The suction and discharge ports 62,63, 121 and 122 function to supply and discharge the working fluid to(from) a pump chamber B formed between the rotor 3 and the cam ring 4.The inlet port IN is connected through a fluid passage 7 a with acontrol valve 7.

The adapter ring 5 is a substantially elliptical annular member having amajor axis along the y-axis and a miner axis along the z-axis. The outercircumferential side (i.e., radially outer side) of the adapter ring 5is surrounded by the inner circumferential surface of the first housing11, and the inner circumferential side (i.e., radially inner side) ofthe adapter ring 5 surrounds or accommodates the cam ring 4. The adapterring 5 is restrained by a pin 40 from rotating relative to the firsthousing 11, namely so as not to rotate within the first housing 11 atthe time of driving operation of the vane pump 1.

The cam ring 4 is an annular member having a substantially completeroundness (i.e., almost perfect circle). An outer diameter of cam ring 4is substantially equal to the miner axis of elliptic bore of the adapterring 5. Since the cam ring 4 is received inside the substantiallyelliptical adapter ring 5, a fluid pressure chamber “A” is formedbetween an inner circumferential surface 53 of the adapter ring 5 and anouter circumferential surface of the cam ring 4. The cam ring 4 can beswung in the direction of y-axis within the adapter ring 5.

As shown in FIG. 2, a sealing member 50 is provided in az-axis-positive-directional end portion of the inner circumferentialsurface 53 of adapter ring 5. On the other hand, the adapter ring 5 isformed with a supporting surface N at a z-axis-negative-directional endportion. Specifically, the sealing member 50 is located in the mostadvanced position of the inner circumferential surface 53 of adapterring 5 in the positive direction of z-axis, and the supporting surface Nis located in the most advanced position of the inner circumferentialsurface 53 of adapter ring 5 in the negative direction of z-axis. Thecam ring 4 is swingable about a swing fulcrum given on the supportingsurface N. The cam ring 4 is in contact with the supporting surface Nand is swingably supported on the supporting surface N of the adapterring 5 in the negative direction of z-axis.

A pin (a second sealing member) 40 is provided in the supporting surfaceN. The pin 40 and the sealing member 50 cooperate with each other todivide the fluid pressure chamber “A” defined by the cam ring 4 and theadapter ring 5 into a first fluid pressure chamber A1 and a second fluidpressure chamber A2. That is, since the first fluid pressure chamber A1is separated from the second fluid pressure chamber A2 by means of thepin 40 and sealing member 50; the first fluid pressure chamber A1 isformed on the y-axis negative side, and the second fluid pressurechamber A2 is formed on the y-axis positive side.

Since the cam ring 4 swings by rolling on the supporting surface N,volumetric capacities of the respective fluid pressure chambers A1 andA2 are varied. As shown in FIG. 2, the supporting surface N is inparallel with ξ-axis which is defined by rotating y-axis about an originpoint of the coordinate system in a counterclockwise direction of FIG.2. That is, the supporting surface N is inclined in the z-axis positivedirection, and thereby a y-axis positive side of the supporting surfaceN is located at a more positive position of z-axis than a y-axisnegative side of the supporting surface N. Accordingly, the cam ring 4has a tendency to swing in the y-axis negative direction because of theinclined supporting surface N.

An outer diameter of the rotor 3 is smaller than a diameter of an innercircumference (surface) 41 of cam ring 4. The rotor 3 is disposed withina central bore of the cam ring 4. The rotor 3 is arranged so as toprevent the outer circumference of rotor 3 from abutting on the innercircumference 41 of cam ring 4 even when the swing movement of cam ring4 varies a relative position between the rotor 3 and cam ring 4.

When the cam ring 4 has moved to its swing position farthest in they-axis negative direction, a distance (radial interval of a pump chamberBy−) L between the inner circumference 41 of cam ring 4 and the outercircumference of rotor 3 becomes maximum on the y-axis negative side. Onthe other hand, when the am ring 4 has moved to its swing positionfarthest in the y-axis positive direction, the distance L becomesmaximum on the y-axis positive side.

Each vane 32 is designed to have a radial length larger than a maximumvalue of the distance (radial interval) L. Hence, each vane 32 remainsin the state where a radially inner portion of vane 32 has been insertedor received in the corresponding slot 31 and a radially outer portion ofvane 32 is in contact with the inner circumference 41 of cam ring 4,regardless of the relative position between the rotor 3 and cam ring 4.Accordingly, the back pressure is always applied from each back pressurechamber 33 to the corresponding vane 32 so that the vane 32 isfluid-tightly in contact with the inner circumference 41 of cam ring 4.

Therefore, a space between the rotor 3 and cam ring 4 is divided intopump chambers B by the vanes 32 which are disposed adjacent to eachother in the circumferential direction of the cam ring 4 and rotor 3.Each pump chamber B formed by the adjacent vanes 32 is always keptfluid-tight. That is, the cam ring 4 cooperates with the rotor 3 andvanes 32 to define the pump chambers B on the inner circumferential sideof cam ring 4. A volume of each pump chamber B varies in accordance withthe rotation of the rotor 3 in the case where the cam ring 4 and therotor 3 are positioned in the eccentric relation to each other as aresult of the swing of cam ring 4.

The suction ports 62 and 121 and the discharge ports 63 and 122 whichare provided respectively in the pressure plate 6 and the second housing12 as mentioned above are formed along the outer circumference of rotor3. The suction ports 62 and 121 are open to a region (some chambers) ofthe plurality of pump chambers B in which the volume of pump chamber Bincreases with the rotation of rotor 3, as shown in FIG. 2. Moreover,the discharge ports 63 and 122 are open to a region (some chambers) ofthe plurality of pump chambers B in which the volume of pump chamber Bdecreases with the rotation of rotor 3. The supply and discharge of theworking fluid are performed through these ports 62, 63, 121 and 122 bythe variation in volume of each pump chamber B.

The adapter ring 5 has a radial through-hole 51 at an end portionthereof in the y-axis positive direction. Moreover, the first housing 11has a plug-member insertion hole 114 at an end portion thereof in they-axis positive direction. A plug member 90 shaped like a cup having itsbottom is inserted in the plug-member insertion hole 114, and serves tokeep the first and second housings 11 and 12 fluid-tightly against anexternal thereof.

A spring 91 is installed radially inside an inner circumference of theplug member 90 (i.e., is installed in an inside bore of plug member 90)and is expandable and compressible in the y-axis direction. The spring91 extends through the radial through-hole 51 of adapter ring 5, andabuts on the cam ring 4. Thereby, the spring 91 biases or urges the camring 4 in the y-axis negative direction.

The spring 91 biases the cam ring 4 in the y-axis negative direction,namely, in the direction causing an amount of swing movement of cam ring4 to become maximum (maximum eccentricity). This biasing force of spring91 serves to stabilize the swing position of cam ring 4 at the time ofstart-up of vane pump 1 during which the fluid pressure is unstable.That is, the spring 91 serves to stabilize the flow rate of workingfluid to be discharged at the time of start-up of vane pump 1.

[Control Valve]

The control valve 7 (corresponding to a pressure control sectionaccording to the present invention) is a mechanical valve adapted to bedriven based on discharge and suction pressures. The first housing 11 isformed with a valve installation hole 115 located in a z-axis positiveportion of first housing 11. The control valve 7 is received orinstalled in the valve installation hole 115. This control valve 7includes a spool 71 and a spring 72. Radially inside the spool 71 formedin a tubular shape having its bottom, a relief valve 80 is installed.

(Spool)

The spool 71 is a hollow cylindrical (tubular) member having one closedend, namely its bottom portion 71 a. The bottom portion 71 a is locatedat an end portion of the spool 71 in the y-axis negative direction. Atanother end portion of the spool 71 in the y-axis positive direction,namely at an opening portion 71 b of the spool 71; the spring 72 biasesthe spool 71 in the y-axis negative direction. Moreover, an outercircumference of the spool 71 includes a sealing portion 71 c which isfluid-tightly in contact with an inner circumferential surface of thevalve installation hole 115.

The opening portion 71 b is also fluid-tightly in contact with the innercircumferential surface of the valve installation hole 115. Hence, thespool 71 divides the valve installation hole 115 into threecompartments, namely, a high pressure chamber C_(H), a medium pressurechamber C_(M) and a low pressure chamber C_(L) which are sealed againstone another. The high pressure chamber C_(H) is formed on the y-axisnegative side of the spool 71. The medium pressure chamber C_(M) isformed on the y-axis positive side of the spool 71. The low pressurechamber C_(L) is formed on the outer circumferential surface of thespool 71 and between the sealing portion 71 c and the opening portion 71b (i.e., spool 71's outer peripheral area surrounded by the sealingportion 71 c, the opening portion 71 b and the first housing 11).

The valve installation hole 115 is connected through a fluid passage 113and a through-hole 52 with the first fluid pressure chamber A1. Thefirst housing 11 is formed with this fluid passage 113. The through-hole52 is a radial through-hole provided in the adapter ring 5. The sealingportion 71 c of spool 71 is located at its position closing the fluidpassage 113 when the spring 72 is not compressed.

Therefore, when the spool 71 moves in the y-axis positive direction, thefluid passage 113 is communicated (or linked) with the high pressurechamber C_(H) so that a high pressure is introduced into the first fluidpressure chamber A1. On the other hand, when the spool 71 moves in they-axis negative direction, the fluid passage 113 is communicated withthe low pressure chamber C_(L) so that a low pressure is introduced intothe first fluid pressure chamber A1.

A y-axis negative portion of the high pressure chamber C_(H) isconnected through a pilot orifice 300 and a fluid passage 21 with thedischarge ports 63 and 122. The low pressure chamber C_(L) is connectedthrough the fluid passage 7 a with the inlet port IN. This fluid passage7 a is provided at a more positive position than the sealing portion 71c relative to y-axis, and hence is not connected with the high pressurechamber C_(H).

The medium pressure chamber C_(M) is connected through a fluid passage116 and a damper orifice 200 with the second fluid pressure chamber A2.Moreover, the second fluid pressure chamber A2 is connected through ametering orifice 110 with a discharge passage 22 and the discharge ports63 and 122. The metering orifice 110 is provided in the pressure plate6. Accordingly, the fluid pressures of the high pressure chamber C_(H)and medium pressure chamber C_(M) correspond respectively to an upstream(fluid) pressure and a downstream pressure of the metering orifice 110.A pressure difference between the upstream pressure and the downstreampressure is proportional to a flow rate (flow quantity) of the meteringorifice 110.

[Swing of Cam Ring]

A control fluid pressure of the control valve 7 is introduced throughthe fluid passage 113 and through-hole 52 into the first fluid pressurechamber A1. Moreover, the downstream pressure of the metering orifice110 is introduced in the second fluid pressure chamber A2.

In accordance with an increase of the discharge pressure; the fluidpressure difference of the metering orifice 110 becomes greater, so thatthe pressure difference between the high pressure chamber C_(H)connected to the upstream side of the metering orifice 110 and themedium pressure chamber C_(M) connected to the downstream side of themetering orifice 110 also becomes greater. This pressure differencemoves the spool 71 of control valve 7 in the y-axis positive directionagainst the biasing force of the spring 72. Thereby, the first fluidpressure chamber A1 is communicated with the high pressure chamber C_(H)so that a high pressure Ph is introduced into the first fluid pressurechamber A1.

Meanwhile, the downstream pressure of the metering orifice 110 isintroduced in the second fluid pressure chamber A2 communicating withthe medium pressure chamber C_(M). Thereby, the pressure differencebetween the first and second fluid pressure chambers A1 and A2 is caused(becomes greater). This pressure difference swings the cam ring 4 in they-axis positive direction against the biasing force of the spring 91.

As a result, the pump chamber By− located on the y-axis negative side isreduced, so that a quantity of working fluid which is pushed (squeezed)into the discharge ports 63 and 122 is reduced. Meanwhile, a pumpchamber By+ located on the y-axis positive side is enlarged, so that aquantity of working fluid which is put back (brought back) to thesuction ports 62 and 121 is increased. Thus, a pump discharge rate(discharge quantity) is reduced, and thereby the pressure difference ofthe metering orifice 110 is reduced so as to reduce the pressuredifference between the high pressure chamber C_(H) and the mediumpressure chamber C_(M).

Accordingly, the spool 71 becomes incapable of resisting the biasingforce of the spring 72, and thereby moves in the y-axis negativedirection. Then, the communication between the first fluid pressurechamber A1 and the high pressure chamber C_(H) is blocked so that thefluid pressure of the first fluid pressure chamber A1 is lowered.Accordingly, the pressure difference between the first fluid pressurechamber A1 and the second fluid pressure chamber A2 is reduced, and they-axis positive directional force caused by this pressure differencebecomes balanced (or matched) with the biasing force of spring 91.Thereby, the swing of the cam ring 4 is stopped.

As explained above, the pressure difference of the metering orifice 110and the biasing forces of springs 72 and 91 function to adjust theposition of cam ring 4 so as to always maintain a constant dischargerate (discharge quantity). In the case that an opening area of themetering orifice 110 is small, the pressure difference becomes large. Inthe case that the opening area of the metering orifice 110 is large, thepressure difference becomes small.

(Relief Valve)

The relief valve 80 includes a valve body 81, a valve seat 82, a valveball 83 and a spring 84. One end of the spring 84 is fixedly connectedwith the bottom portion 71 a of the spool 71. The spring 84 biases orurges the valve body 81 in the y-axis positive direction. Thereby, thevalve body 81 is in contact with the valve ball 83, and biases the valveseat 82 in the y-axis positive direction through this valve ball 83.

An outer circumferential surface of a y-axis positive-directional endportion 81 a of the valve body 81 is fluid-tightly in contact with aninner circumferential surface of the spool 71. Hence, the valve body 81cooperates with the inner circumference of the spool 71 to define afirst fluid chamber D1. The spool 71 is formed with a first radial hole71 d provided from the outer circumference of the spool 71. The firstradial hole 71 d connects the inner circumferential surface of spool 71with the outer circumferential surface of spool 71 to communicate aninside space of spool 71 to an outside space of spool 71.

When the spring 84 of relief valve 80 is under its most expanded state(i.e., when the spring 84 has expanded to a greatest extent), the firstradial hole 71 d is located at a more negative position relative toy-axis than the end portion 81 a of the valve body 81. At this time, thefirst radial hole 71 d communicates the low pressure chamber C_(L) withthe first fluid chamber D1. When the valve body 81 moves in the y-axisnegative direction, the first radial hole 71 d is closed.

The valve seat 82 includes a through-hole 82 a formed in the y-axisdirection. At a y-axis negative side of this through-hole 82 a, thethrough-hole 82 a is closed or blocked by the valve ball 83 providedbetween the through-hole 82 a and the valve body 81. A y-axis positiveportion of the valve seat 82 faces the medium pressure chamber C_(M).The outer circumference of the valve seat 82 is fixed to the innercircumference of the spool 71 by means of press fitting, and thereby asecond fluid chamber D2 is formed between the valve body 81 and thevalve seat 82.

Since the through-hole 82 a is provided in the valve seat 82 in they-axis direction, a medium pressure Pm is applied through thethrough-hole 82 a to the valve ball 83 in the y-axis negative direction.When the medium pressure Pm within the medium pressure chamber C_(M)increases, the valve ball 83 is pressed in the y-axis negative directionagainst the biasing force of spring 84. Thereby, the valve ball 83 isdetached (moves apart) from the through-hole 82 a, so that the mediumpressure chamber C_(M) is communicated with the low pressure chamberC_(L). Thus, a relief state is achieved, in which the medium pressure Pmis drained through the fluid passage 7 a to the inlet port IN.

(Swing of Cam Ring at the Time of Relief)

Since the fluid passage 116 and damper orifice 200 are provided upstreamof the medium pressure chamber C_(M), the fluid pressure of mediumpressure chamber C_(M) is reduced at the time of the relief state.Thereby, the pressure difference between the medium pressure chamberC_(M) and the high pressure chamber C_(H) becomes larger so that thespool 71 moves in the y-axis positive direction by resisting against thebiasing force of spring 72.

Then, the first fluid pressure chamber A1 is made to communicate withthe high pressure chamber C_(H). Because of this high pressure, the camring 4 is swung in the y-axis positive direction, so that the dischargeflow rate is reduced. Because of the reduction of discharge flow rate,the pressure difference of the metering orifice 110 is reduced so thatthe pressure difference between the medium pressure chamber C_(M) andthe high pressure chamber C_(H) is reduced. Thereby, the pressure Ph ofhigh pressure chamber C_(H) becomes unable to resist the biasing forceof spring 72, so that the spool 71 moves in the y-axis negativedirection.

Thereby, the communication between the high pressure chamber C_(H) andthe first fluid pressure chamber A1 is blocked, and the pressure of thefirst fluid pressure chamber A1 is lowered. At this time, the y-axispositive-directional force which is applied from the first fluidpressure chamber A1 to the cam ring 4 is reduced so that the swing ofcam ring 4 stops. Thus, the discharge flow rate is reduced.

Thereby, the pressure difference between upstream and downstream sidesof the metering orifice 110 is also reduced. That is, the enlargement ofthis pressure difference between the upstream and downstream sides iscorrected, so that the pump discharge flow rate is maintained to apredetermined flow rate. Therefore, under the relief state, a surplusflow rate (quantity) is reduced by means of the swing of cam ring 4 soas to improve an efficiency.

(Metering Orifice)

FIG. 3 is an enlarged cross-sectional view near a variable metering(throttling) mechanism 100. The metering orifice 110 is a long (andnarrow) hole formed long in the circumferential direction of vane pump1. An opening area of the metering orifice 110 is varied by they-axis-directional swing of the cam ring 4.

The long hole defining the metering orifice 110 is designed to cause amajor (longer) axis of the metering orifice 110 to deviate slightly fromthe z-axis direction. That is, the major axis of the metering orifice110 is inclined from a cam ring 4's tangent which is perpendicular to animaginary line passing through a center point of the major axis ofmetering orifice 110 and the center Oc of cam ring 4. A portion 111 of az-axis negative-directional end portion of the metering orifice 110 isnot closed by the cam ring 4 even when the cam ring 4 swings in they-axis positive direction to its greatest extent, as shown in FIG. 3.Hence, the metering orifice 110 is always open to the second fluidpressure chamber A2 at least by the minimum secured area 111. That is,the minimum secured area 111 which is not blocked by the cam ring 4always communicates with the second fluid pressure chamber A2.

When the cam ring 4 swings in the y-axis positive direction, the openingportion of the metering orifice 110 is partly closed by the cam ring 4to reduce the opening area of metering orifice 110. When the cam ring 4reaches its position farthest in the y-axis positive direction, themetering orifice 110 is closed except only one portion (minimum securedarea 111). This variable metering mechanism 100 adapted to vary the areaof flow passage is achieved by the metering orifice 110 and the cam ring4.

Since the opening portion of the metering orifice 110 is provided in theshape of a long narrow hole (elliptical slot) elongated in thecircumferential direction of cam ring 4, the metering orifice 110 isgradually closed after the cam ring 4 has swung by a predeterminedangle. Therefore, the metering orifice 110 is not closed or narroweddown at the time of a non-relief state where the discharge flow rate isconstant. Thereby, it is suppressed that the discharge-rate control isinfluenced by the variation of the pressure difference between upstreamand downstream sides of the metering orifice 110. Thereby, a tuning ofthe discharge-rate control is made easy to conduct.

Moreover, since the opening portion of the metering orifice 110 isshaped like a long hole having the greater circumferential width thanthe radial width thereof as mentioned above, the opening area of themetering orifice 110 can be reduced rapidly relative to an amount(displacement) of swing of the cam ring 4.

[Fluid Pressure Supply to First and Second Fluid Pressure Chambers]

The discharge pressure is restricted by the pilot orifice 300 providedon the fluid passage 21, and then is supplied to the high pressurechamber C_(H) so as to urge the spool 71 in the y-axis positivedirection. Thereby, the spool 71 moves in the y-axis positive directionso that the high pressure chamber C_(H) is communicated with the fluidpassage 113. Accordingly, the pressure Ph of high pressure chamber C_(H)is introduced into the first fluid pressure chamber A1. The dischargepressure is also introduced to the discharge passage 22, and then isintroduced into the second fluid pressure chamber A2 by being restrictedby the metering orifice 110, as shown in FIG. 2.

Since the fluid pressure of second fluid pressure chamber A2 is suppliedto a fluid-pressure available pathway (connected to a pressure-usingdevice) provided outside the vane pump 1, the orificepressure-difference occurs in proportion to the flow rate of themetering orifice 110. Thereby, the medium pressure Pm of medium pressurechamber C_(M) located downstream of the metering orifice 110 becomeslower than the pressure Ph of high pressure chamber C_(H) locatedupstream of the metering orifice 110. Accordingly, the second fluidpressure chamber A2 is made to have a lower pressure than that of thefirst fluid pressure chamber A1 so that the cam ring 4 swings in they-axis positive direction.

When the cam ring 4 swings; the pump discharge flow rate decreases, andthe flow-rate pressure difference of the metering orifice 110 islowered. Thereby, the pressure difference between the high pressurechamber C_(H) and the medium pressure chamber C_(M) is reduced so thatthe biasing force of spring 72 moves the spool 71 in the y-axisdirection. Thereby, the pressure to be supplied to the first fluidpressure chamber A1 is reduced, so that the swing of cam ring 4 isstopped. Thus, the predetermined discharge flow rate is attained.

The outer circumferential side of cam ring 4 receives the pressures offirst and second fluid pressure chambers A1 and A2, and the innercircumferential side of cam ring 4 receives the discharge pressure inthe y-axis negative direction and also in the z-axis negative direction.The swing of cam ring 4 is stopped at a position striking a balanceamong these pressures.

In the case that the discharge rate decreases, because of the reductionof pressure difference of the metering orifice 110, the pressure Phwithin high pressure chamber C_(H) is also reduced. Thereby, the spool71 is moved in the y-axis negative direction by the biasing force ofspring 72 so that the low pressure chamber C_(L) is communicated withthe fluid passage 113. Thereby, a low pressure Pl is introduced into thefirst fluid pressure chamber A1, so that the first fluid pressurechamber A1 becomes lower in fluid pressure than the second fluidpressure chamber A2. Accordingly, the cam ring 4 returns in the y-axisnegative direction. Thus, the pressure difference of the meteringorifice 110 becomes constant to attain or maintain the predeterminedflow rate.

[Reduction of Discharge Flow Rate During Relief State]

FIG. 4 is a view showing a relation between the opening area of meteringorifice 110 and the swing amount of cam ring 4 (the position of cam ring4 by its swing motion). In the case where the swing amount of cam ring 4is within a normal use range; the metering orifice 110 is not closed bythe cam ring 4, namely, the opening area of metering orifice 110 remainsconstant in its fully open condition. Accordingly, the discharge flowrate is maintained at a constant flow rate, by means of the movement ofspool 71, the swing of cam ring 4 and the pressure difference ofmetering orifice 110.

In the case of relief state where the pressure of medium pressurechamber C_(M) is drained through the relief valve 80 and the fluidpassage 7 a to the inlet port IN, the pressure of medium pressurechamber C_(M) is reduced because of the existence of the fluid passage 7a and the pilot orifice 300.

Thereby, the pressure Ph of high pressure chamber C_(H) becomes higherthan the pressure Pm of medium pressure chamber C_(M), so that thepressure P1 of first fluid pressure chamber A1 communicating with thehigh pressure chamber C_(H) becomes higher than the pressure P2 of thesecond fluid pressure chamber A2 communicating with the medium pressurechamber C_(M). Accordingly, the cam ring 4 swings in the y-axis positivedirection, so that the discharge rate is reduced. Here, under the reliefstate, the swing amount (i.e., displacement in the y-axis positivedirection) of cam ring 4 is further enlarged as mentioned above.

Since the cam ring 4 moves in the y-axis positive direction, the openingarea of metering orifice 110 is reduced. Since the opening area ofmetering orifice 110 is reduced, the pressure difference between theboth sides of metering orifice 110 is increased. Accordingly, thepressure difference between the high pressure chamber C_(H) and themedium pressure chamber C_(M) is also increased. Hence, the spool 71moves in the y-axis positive direction so that the high pressure chamberC_(H) is communicated with the first fluid pressure chamber A1. Sincethe pressure P1 of first fluid pressure chamber A1 rises, the cam ring 4further swings in the y-axis positive direction so that the dischargeflow rate is further reduced.

As explained above, at the time of relief state, the surplus quantity ofworking fluid which is drained from the medium pressure chamber C_(M) tothe inlet port IN is reduced by restricting the flow rate to the mediumpressure chamber C_(M). Thus, the drain quantity of working fluid isreduced during the relief state so as to enhance fuel economy.

In this embodiment, the swing of cam ring 4 varies the cross sectionalarea of flow passage (the opening area of metering orifice 110), andthereby the drain quantity of working fluid is reduced. Therefore, thedrain quantity of working fluid is linked to the variation of crosssectional area of flow passage with the use of simple structure.

Moreover, by providing the pilot orifice 300, the cam ring 4 is madeeasy to move in the y-axis positive direction so that the opening areaof metering orifice 110 is made easy to be narrowed or reduced. Thereby,the drain quantity of working fluid is further reduced at the time ofrelief. At that time, the relief state can be accurately judged orrecognized by detecting the y-axis positive-directional movement(position) of cam ring 4.

In case that the pilot orifice 300 is more narrowed down, it isconceivable that the pressure Pm of medium pressure chamber C_(M)becomes further easy to be reduced at the time of relief state, andthereby the swing amount of cam ring 4 is made greater to further reducethe surplus flow rate. However in such a case, there is a fear that avibration of valve ball 83 under the relief state fluctuates thepressure Pm of medium pressure chamber C_(M) so as to also vibrate thespool 71 and cam ring 4. Thereby, there is a fear that a vibration ofthe discharge pressure is caused.

Therefore, in this embodiment according to the present invention, thestructure is employed which lessens the metering orifice 110 at the timeof relief state. According to this structure, the lessening(narrowing-down) of the pilot orifice 300 can be set relativelymoderately. In this embodiment, the surplus flow rate is reduced withoutcausing the vibration of fluid pressure.

Moreover, by providing the damper orifice 200; a vibration of spool 71which is caused due to the discharge pressure is suppressed, and alsothe fluid-pressure vibration at the time of relief state is suppressedso that the control valve 7 operates stably resulting in a stable swingof cam ring 4.

[Structures and Effects According to First Embodiment]

(1) The variable displacement vane pump in the first embodiment includesthe metering orifice 110 formed on the discharge passage 22 connectedwith the discharge ports 63 and 122; the control valve 7 adapted tocontrol the pressure which is introduced into the first fluid pressurechamber A1 or the second fluid pressure chamber A2, wherein the controlvalve 7 includes the high pressure chamber C_(H) into which the upstreampressure of the metering orifice 110 is introduced, the medium pressurechamber C_(M) into which the downstream pressure of the metering orifice110 is introduced, and the low pressure chamber C_(L) connected with thereservoir tank RSV for storing working fluid; the relief valve 80provided between the downstream side of metering orifice 110 and thereservoir tank RSV, wherein the relief valve 80 is adapted to be openedby receiving a pressure greater than or equal to a predetermined leveland thereby to drain the downstream pressure of the metering orifice 110to the reservoir tank RSV; and the variable metering mechanism 100configured to narrow the cross-sectional area of opening portion (flowpassage) of the metering orifice 110 at least when the relief valve 80is opened.

Accordingly, it becomes possible that the flow rate is reduced by themetering orifice 110 at the time of relief so that the cam ring 4 isswung. Thereby, the surplus fluid quantity to be drained from the mediumpressure chamber C_(M) to the inlet port IN is reduced. Thus, thesurplus flow rate can be stably reduced without generating thefluid-pressure vibration. Therefore, the increase in pump workload canbe suppressed while reducing the relief amount, and thereby the fueleconomy is enhanced.

(2) The cam ring 4 is adapted to swing so as to gradually block theopening portion of the metering orifice 110, and hence the variablemetering mechanism 100 is achieved by the metering orifice 110 and thecam ring 4. Further, the opening portion of metering orifice 110 isformed in the axial end surface of the first plate member 12 or thesecond plate member 6. Accordingly, the reduction of drain flow rate ofworking fluid can be linked to the variation of cross sectional area ofthe flow passage under the relief state, with the use of simplestructure.

(3) The variable metering mechanism 100 is configured to graduallynarrow the opening portion of the metering orifice 110 after the camring 4 has swung to its position having a predetermined angle.Accordingly, the metering orifice 110 is not blocked or narrowed at thetime of non-relief state where the discharge flow rate is constant.Thereby, it is suppressed that the discharge-rate control is influencedby the variation of the pressure difference between upstream anddownstream sides of the metering orifice 110. Thereby, the tuning of thedischarge-rate control can be made easy to perform.

(4) The circumferential width of opening portion of the metering orifice110 is greater than the radial width thereof. Accordingly, the area ofthe metering orifice 110 can be narrowed sharply for the swing amount ofthe cam ring 4 so as to greatly reduce the surplus flow rate.

(5) The opening portion of the metering orifice 110 is formed in anelliptical shape or a slot shape. Accordingly, the area of the meteringorifice 110 can be narrowed sharply for the swing amount of the cam ring4 so as to greatly reduce the surplus flow rate.

(6) The variable displacement vane pump further includes a pilot orifice300 provided on the passage connecting the discharge ports 63 and 122with the high pressure chamber C_(H). Accordingly, the relief state canbe accurately judged based on the swing motion of cam ring 4.

(7) The variable displacement vane pump further includes the damperorifice 200 provided on the passage connecting the metering orifice 110with the medium pressure chamber C_(M). Accordingly, the stability ofcontrol valve 7 can be improved at the time of relief.

Other modified examples according to the first embodiment will beexplained below.

[First Modified Example According to First Embodiment]

FIGS. 5 and 6 show an example in which the minimum secured area 111 ofmetering orifice 110 is provided as a separate hole (another hole).Although the major axis of the metering orifice 110 (i.e., the longeraxis of cross-section of metering orifice 110) is inclined from thez-axis in the above-mentioned example of the first embodiment, themetering orifice 110 in the first modified example of the firstembodiment is formed as a long hole (slot) having its major axisparallel to the z-axis. In the first modified example, the hole (anotherhole) formed separately on the y-axis positive side of the meteringorifice 110 serves as the minimum secured area 111.

The metering orifice 110 is completely closed when the cam ring 4reaches its most positive swing position relative to y-axis, namely iscompletely closed at the position of an alternate long and two shortdashes line of FIG. 6. On the other hand, the minimum secured area 111is located at a position which is not closed irrespective of the swingposition of cam ring 4. Therefore, the major (longer) axis of meteringorifice 110 is provided in parallel with the z-axis so that amanufacturing processing of the metering orifice 110 can be simplified.

[Second Modified Example According to First Embodiment]

FIG. 7 shows an example in which the metering orifice 110 is provided asa plurality of holes each having a substantially complete roundness.Accordingly, a sufficient opening area can be ensured as well asensuring a stiffness near the opening portion of metering orifice 110.

[Third Modified Example According to First Embodiment]

FIG. 8 shows an example further modifying the above-explained firstmodified example in such a manner that the damper orifice 200 isprovided outside the adapter ring 5. In the third modified example, afluid passage 23 connecting the second fluid pressure chamber A2 withthe medium pressure chamber C_(M) is provided outside the first housing11, and this fluid passage 23 is formed with the damper orifice 200.

[Fourth Modified Example According to First Embodiment]

FIG. 9 shows an example in which a piston 92 adapted to move in and outin response to the swing of cam ring 4 is provided, and this piston 92is formed with the metering orifice 110. The piston 92 is located on they-axis negative side of the plug member 90 and on the y-axis positiveside of the cam ring 4. The piston 92 is a circular tubular (hollowcylindrical) member having its bottom. The bottom portion of piston 92abuts on the cam ring 4 in the y-axis negative direction.

An outer circumferential surface of piston 92 is inserted into theplug-member insertion hole 114 slidably and fluid-tightly. Thereby, thepiston 92 cooperates with the plug member 90 to define a third fluidchamber D3. An inner circumference of the plug member 90 is formed withan opening portion 22 a of the discharge passage 22 communicating withthe discharge ports 63 and 122. Thereby, the discharge pressure isintroduced into the third fluid chamber D3, and cooperates with thespring 91 to bias the piston 92 in the y-axis negative direction.Accordingly, the cam ring 4 is biased in the y-axis negative directionthrough the piston 92 by means of the biasing force of spring 91 and thepressure of the third fluid chamber D3.

A tubular portion of the piston 92 is formed with small (through-)holeseach of which communicates an inner circumferential surface of piston 92with an outer circumferential surface of piston 92. These small holesare used as the metering orifice 110. The piston 92 is pressed by thecam ring 4 in the y-axis positive direction in accordance with they-axis positive-directional swing of cam ring 4, and thereby moves inthe y-axis positive direction against the pressures of spring 91 andthird fluid chamber D3.

When the piston 92 moves in the y-axis positive direction, the piston 92is deeply inserted (buried) into the plug-member insertion hole 114.Thereby, the metering orifice 110 is closed by (the inner surface of)the plug-member insertion hole 114. In such a way, the variable meteringmechanism 100 is constructed in the fourth modified example.Accordingly, the drain quantity of working fluid is reduced at the timeof relief state in the similar manner as the not-modified example of thefirst embodiment. In this fourth modified example, since the meteringorifice 110 is closed by the plug-member insertion hole 114, a leakagein the metering orifice 110 becomes relatively low so that an accuracyin the quantity metering (reduction) control is enhanced.

(8) The variable displacement vane pump according to the firstembodiment further includes the piston 92 adapted to move in response tothe swing of cam ring 4; and the metering orifice 110 is formed in thepiston 92. Accordingly, the leakage of the metering orifice 110 becomesrelatively small so that the accuracy in quantity metering (reduction)control can be enhanced.

Second Embodiment

A second embodiment according to the present invention will now beexplained. A basic structure of the second embodiment is similar as thefirst embodiment. Although the opening portion provided on the dischargepassage 22 is used as the metering orifice 110 in the first embodiment,a spool 400 adapted to vary an area of flow passage corresponds to themetering orifice 110, in the second embodiment, as a different pointfrom the first embodiment.

FIG. 10 is a cross-sectional view of vane pump 1 according to the secondembodiment, taken in the axial direction of vane pump 1. FIG. 11 is across-sectional view of the vane pump 1, taken in the radial directionof vane pump 1. Since the cross section of FIG. 11 is different from thecross section (FIG. 2) taken in the axial direction in the firstembodiment, only a part of the control valve 7 is shown in FIG. 11. Thefirst housing 11 is formed with a spool installation hole 117 located inparallel with the valve installation hole 115 for the control valve 7.The spool 400 is installed or received in this spool installation hole117.

The spool 400 includes step portions 423 and 425 at both end portions ofspool 400 in the y-axis direction. The spool 400 further includes arecess portion 424 in a substantially center portion of spool 400. Thisrecess portion 424 is formed in the entire outer circumference (i.e.,all-around) of spool 400. Moreover, sealing portions 421 and 422 areprovided to the outer circumferential surface of spool 400 on y-axisdirectional both sides of the recess portion 424. Accordingly, the spoolinstallation hole 117 is divided into three compartments, namely, afirst spool fluid chamber 411, a second spool fluid chamber 412 and athird spool fluid chamber 413 which are sealed fluid-tightly against oneanother.

A spring 401 is provided in the first spool fluid chamber 411. One endof spring 401 is engaged with the step portion 423 located at the y-axisnegative portion of the spool 400, and another end of spring 401 isfixed to a y-axis negative end portion of the spool installation hole117. Thereby, the spool 400 is biased in the y-axis positive direction.The first spool fluid chamber 411 is connected with the inlet port IN,and thereby the suction pressure is introduced into the first spoolfluid chamber 411. The first spool fluid chamber 411 is also connectedthrough the fluid passage 7 a with the low pressure chamber C_(L) of thecontrol valve 7.

The second spool fluid chamber 412 and third spool fluid chamber 413 areconnected with the outlet port OUT. Thereby, the discharge pressure isintroduced into the second spool fluid chamber 412 and third spool fluidchamber 413 so that the spool 400 is biased in the y-axis negativedirection. The outlet port OUT is connected with the discharge ports 63and 122 and the medium pressure chamber C_(M) through fluid passages(not shown).

The second fluid pressure chamber A2 is connected through a fluidpassage 24 with the spool installation hole 117. An opening portion 24 aof the fluid passage 24 which is open to the spool installation hole 117is provided to overlap with the recess portion 424 in the z-axisdirection under a normal state where a sufficient pressure difference isnot applied to the spool 400. Specifically, y-axis directional positionsof both ends of opening portion 24 a are same as y-axis directionalpositions of both ends of recess portion 424 under the normal state.Accordingly, the fluid passage 24 is connected through the recessportion 424 with the outlet port OUT, under the normal state.

When the discharge pressure becomes higher and reaches the reliefpressure, the spool 400 moves in the y-axis negative direction againstthe biasing force of spring 401. Thereby, the opening portion 24 a isgradually closed or narrowed by the sealing portion 422 of spool 400which is located on the y-axis positive side of the recess portion 424.Accordingly, the area of flow passage between the second fluid pressurechamber A2 and the outlet port OUT is reduce (corresponding to thenarrowing of metering orifice 110 in the first embodiment), so that the(some) pressure difference between the second fluid pressure chamber A2and the outlet port OUT is caused. This pressure difference moves thecontrol valve 7, so that the pressure Ph of high pressure chamber C_(H)is introduced into the first fluid pressure chamber A1.

Thereby, the cam ring is swung in the y-axis positive direction, so thatthe discharge rate (discharge quantity) and the discharge pressure arereduced. Accordingly, the surplus discharge pressure at the time ofrelief is reduced in the similar manner as the first embodiment. Thebiasing force of spring 401 is adjusted to allow the narrowing of theopening portion 24 a to start when the discharge pressure becomesgreater than or equal to a predetermined value. Hence, in this secondembodiment, the variable metering mechanism 100 is constructed by use ofa convenient structure. Moreover, the surplus flow rate is cut reliablyat the time of relief pressure.

[Structures and Effects According to Second Embodiment]

(1) The variable displacement vane pump in the second embodimentincludes the variable metering mechanism 100 configured to narrow thecross-sectional area of opening portion (flow passage) of the meteringorifice 24 a when the discharge pressure on the downstream side of thedischarge ports 63 and 122 is higher than or equal to a predeterminedpressure. Accordingly, the similar effects as in the first embodimentcan be obtained.

(2) The variable metering mechanism 100 is achieved by the spool 400adapted to controllably vary the opening area of the metering orifice 24a by moving relative to the metering orifice 24 a. Accordingly, thevariable metering mechanism 100 can be simply constructed.

Other modified examples according to the second embodiment will beexplained below.

[First Modified Example According to Second Embodiment]

FIG. 12 show an example in which the spool 400 is provided as anelectromagnetic (solenoid) valve. In the above-explained non-modifiedexample of the second embodiment, the spool 400 is a mechanical valveadapted to move based on the discharge pressure. On the other hand, in afirst modified example of the second embodiment, the spool 400 isconstructed by the electromagnetic valve and is connected with anelectromagnetic actuator 500. Moreover, there is provided a pressuresensor 510 for sensing the pressure of the outlet port OUT. Theelectromagnetic actuator 500 is driven based on the sensed values ofpressure sensor 510, and thereby narrows or blocks the opening portion24 a (corresponding to the metering orifice 110 in the first embodiment,i.e., corresponding to the metering orifice according to the presentinvention). Thus, the variable metering mechanism 100 is achieved.

(Structures and Effects According to First Modified Example of SecondEmbodiment)

(3) The variable metering mechanism 100 is achieved by thefluid-pressure sensor 510 adapted to sense the discharge pressure, andthe electromagnetic valve adapted to be opened based on the sensedsignal of the fluid-pressure sensor 510. Accordingly, a freedom degreein design and tuning accuracy can be enhanced since the area of flowpassage is varied by moving the spool 400 electromagnetically.

[Second Modified Example According to Second Embodiment]

FIG. 13 shows an example further modifying the above-explained firstmodified example of second embodiment in such a manner that the reliefvalve 80 is provided outside the housing 11. In a second modifiedexample of the second embodiment, the relief valve 80 is connectedthrough a fluid passage 27 with the second spool fluid chamber 412 ofspool 400 and the medium pressure chamber C_(M). The relief valve 80 isalso connected with a reservoir tank RSV. This relief valve 80 onlypermits a flow from the fluid passage 27 toward the reservoir tank RSV,namely, permits the flow in only one direction.

The second spool fluid chamber 412 of spool 400 is connected through afluid passage 26 with the discharge ports 63 and 122. Moreover, thefirst spool fluid chamber 411 is connected through a fluid passage 28with the inlet port IN.

Since the relief valve 80 is located outside the control valve 7 andthere is no orifice between the medium pressure chamber C_(M) and thefluid passage 27; the reduction of pressure of medium pressure chamberC_(M) due to a narrow shape of orifice is not caused at the time ofrelief state. Thereby, the swing of cam ring 4 is suppressed.

In the second modified example of the second embodiment, when the sensedvalue of pressure sensor 510 reaches the relief pressure, theelectromagnetic actuator 500 is driven to move the spool 400 and therebynarrow the fluid passage 27 (corresponding to the narrowing of meteringorifice 110 in the first embodiment). Thereby, the cam ring 4 is swungso that the surplus flow quantity is reduced. Therefore, it is notnecessary to operate the control valve 7 by using the discharge pressureunder the relief state. Thus, the problem regarding the vibration ofcontrol valve 7 is also avoided.

[Third Modified Example According to Second Embodiment]

FIGS. 14 and 15 show an example in which the shape of the spool 400 ischanged in a manner that the spool 400 is operated by use of a drainpressure produced at a downstream side of the relief valve 80. In athird modified example of the second embodiment, a fluid passage 30 isprovided at the y-axis negative side (end) of the spool 400, as shown inFIG. 15. Through this fluid passage 30, the spool 400 is connected withthe downstream side of the relief valve 80. The spring 401 is providedwithin the third spool fluid chamber 413, and biases the spool 400 inthe y-axis negative direction.

In this third modified example, the spool 400 forms a fourth spool fluidchamber 414 within the spool installation hole 117, in addition to thefirst to third spool fluid chambers 411 to 413. Hence, a volume of thefirst spool fluid chamber 411 is smaller than that of the non-modifiedexample of the second embodiment.

The fourth spool fluid chamber 414 is located between the first andsecond spool fluid chambers 411 and 412, and is connected through afluid passage 29 with the inlet port IN. Moreover, the fourth spoolfluid chamber 414 is connected with the third spool fluid chamber 413through a shaft-center hole 430 formed in a shaft center portion of thespool 400, so that the suction pressure is introduced into the thirdspool fluid chamber 413.

Accordingly, when the downstream pressure of the relief valve 80 becomeshigh, the spool 400 moves in the y-axis positive direction against thebiasing force so that the opening area of the opening portion 24 a offluid passage 24 is reduced. Thus, in the similar manner as thenon-modified example of the second embodiment, the surplus dischargepressure is reduced at the time of relief, and the variable meteringmechanism 100 is constructed by use of a convenient structure.Furthermore, since the spool 400 is driven by using the downstream-sidepressure of relief valve 80, the relief state is more accurately judgedor recognized.

(Structures and Effects According to Third Modified Example of SecondEmbodiment)

(4) The variable metering mechanism 100 is configured to vary the areaof the opening portion (fluid passage) on the basis of the downstreampressure of relief valve 80. Accordingly, the relief state can be moreaccurately caught.

(5) The variable metering mechanism 100 is achieved by the spool 400adapted to controllably vary the opening area by moving in and out.Accordingly, the variable metering mechanism 100 can be simplyconstructed.

Other Embodiments

Although the invention has been described above with reference tocertain embodiments of the invention, the invention is not limited tothe embodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings.

This application is based on prior Japanese Patent Application No.2007-212854 filed on Aug. 17, 2007. The entire contents of this JapanesePatent Application are hereby incorporated by reference.

The scope of the invention is defined with reference to the followingclaims.

1. A variable displacement vane pump comprising: a pump body; a driveshaft supported rotatably by the pump body; a rotor disposed inside thepump body and adapted to be rotatably driven by the drive shaft, therotor being formed with a plurality of slots spaced from each other in acircumferential direction of the rotor; a plurality of vanes received bythe slots so as to be movable out from the slots and into the slots; acam ring formed in an annular shape and disposed inside the pump body topermit the cam ring to become eccentric relative to the drive shaft, thecam ring cooperating with the rotor and the vanes to define a pluralityof pump chambers on an inner circumferential side of the cam ring; afirst plate member and a second plate member disposed on axially bothsides of the cam ring; a suction port provided on a side of at least oneof the first plate member and the second plate member and opened to atleast one of the plurality of pump chambers; a discharge port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; asealing member provided on an outer circumferential side of the camring, the sealing member dividing a space on an outer circumferentialsurface of the cam ring into a first fluid pressure chamber and a secondfluid pressure chamber, wherein a flow rate of working fluid dischargedfrom the discharge port is increased when the cam ring moves to thefirst fluid pressure chamber, wherein the flow rate of working fluiddischarged from the discharge port is decreased when the cam ring movesto the second fluid pressure chamber; a metering orifice formed on adischarge passage connected with the discharge port; a pressure controlsection adapted to control a pressure which is introduced into the firstfluid pressure chamber or the second fluid pressure chamber, thepressure control section comprising a high pressure chamber into whichan upstream pressure of the metering orifice is introduced, a mediumpressure chamber into which a downstream pressure of the meteringorifice is introduced, and a low pressure chamber connected with areservoir tank for storing working fluid; a relief valve providedbetween a downstream side of the metering orifice and the reservoirtank, the relief valve being adapted to be opened by receiving apressure greater than or equal to a predetermined level and thereby todrain the downstream pressure of the metering orifice to the reservoirtank; and a variable metering mechanism configured to narrow across-sectional area of opening portion of the metering orifice at leastwhen the relief valve is opened.
 2. The variable displacement vane pumpas claimed in claim 1, wherein the cam ring is adapted to swing so as togradually block the opening portion of the metering orifice, thevariable metering mechanism being achieved by the metering orifice andthe cam ring; and the metering orifice comprises the opening portionformed in an axial end surface of the first plate member or the secondplate member.
 3. The variable displacement vane pump as claimed in claim2, wherein the variable metering mechanism is configured to graduallynarrow the opening portion of the metering orifice after the cam ringhas swung to its position having a predetermined angle.
 4. The variabledisplacement vane pump as claimed in claim 2, wherein a circumferentialwidth of the opening portion of the metering orifice is greater than aradial width thereof.
 5. The variable displacement vane pump as claimedin claim 4, wherein the opening portion of the metering orifice isformed in an elliptical shape or a slot shape.
 6. The variabledisplacement vane pump as claimed in claim 4, wherein the meteringorifice comprises a plurality of holes.
 7. The variable displacementvane pump as claimed in claim 2, further comprising a pilot orificeprovided on a passage connecting the discharge port with the highpressure chamber.
 8. The variable displacement vane pump as claimed inclaim 2, further comprising a damper orifice provided on a passageconnecting the metering orifice with the medium pressure chamber.
 9. Thevariable displacement vane pump as claimed in claim 1, wherein thevariable displacement vane pump further comprises a piston adapted tomove in response to a swing of the cam ring; and the metering orifice isformed in the piston.
 10. The variable displacement vane pump as claimedin claim 1, wherein the variable metering mechanism is configured tovary the area of opening portion of the metering orifice on the basis ofa downstream pressure of the relief valve.
 11. The variable displacementvane pump as claimed in claim 10, wherein the variable meteringmechanism is achieved by a spool adapted to controllably vary the areaof opening portion of the metering orifice by moving relative to themetering orifice.
 12. A variable displacement vane pump comprising: apump body; a drive shaft supported rotatably by the pump body; a rotordisposed inside the pump body and adapted to be rotatably driven by thedrive shaft, the rotor being formed with a plurality of slots spacedfrom each other in a circumferential direction of the rotor; a pluralityof vanes received by the slots so as to be movable out from the slotsand into the slots; a cam ring formed in an annular shape and disposedinside the pump body to permit the cam ring to become eccentric relativeto the drive shaft, the cam ring cooperating with the rotor and thevanes to define a plurality of pump chambers on an inner circumferentialside of the cam ring; a first plate member and a second plate memberdisposed on axially both sides of the cam ring; a suction port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; adischarge port provided on a side of at least one of the first platemember and the second plate member and opened to at least one of theplurality of pump chambers; a sealing member provided on an outercircumferential side of the cam ring, the sealing member dividing aspace on an outer circumferential surface of the cam ring into a firstfluid pressure chamber and a second fluid pressure chamber, wherein aflow rate of working fluid discharged from the discharge port isincreased when the cam ring moves to the first fluid pressure chamber,wherein the flow rate of working fluid discharged from the dischargeport is decreased when the cam ring moves to the second fluid pressurechamber; a metering orifice formed on a discharge passage connected withthe discharge port; a pressure control section adapted to control apressure which is introduced into the first fluid pressure chamber orthe second fluid pressure chamber, the pressure control sectioncomprising a high pressure chamber into which an upstream pressure ofthe metering orifice is introduced, a medium pressure chamber into whicha downstream pressure of the metering orifice is introduced, and a lowpressure chamber connected with a reservoir tank for storing workingfluid; a relief valve provided between a downstream side of the meteringorifice and the reservoir tank, the relief valve being adapted to beopened by receiving a pressure greater than or equal to a predeterminedlevel and thereby to drain the downstream pressure of the meteringorifice into the reservoir tank; and a variable metering mechanismconfigured to narrow a cross-sectional area of opening portion of themetering orifice when a discharge pressure on a downstream side of thedischarge port is higher than or equal to a predetermined pressure. 13.The variable displacement vane pump as claimed in claim 12, wherein thevariable metering mechanism is achieved by a fluid-pressure sensoradapted to sense the pressure discharged from the discharge port and anelectromagnetic valve adapted to be opened based on a sensed signal ofthe fluid-pressure sensor.
 14. The variable displacement vane pump asclaimed in claim 12, wherein the variable metering mechanism is achievedby a spool adapted to controllably vary the area of opening portion ofthe metering orifice by moving relative to the metering orifice.
 15. Avariable displacement vane pump comprising: a pump body; a drive shaftsupported rotatably by the pump body; a rotor disposed inside the pumpbody and adapted to be rotatably driven by the drive shaft, the rotorbeing formed with a plurality of slots spaced from each other in acircumferential direction of the rotor; a plurality of vanes received bythe slots so as to be movable out from the slots and into the slots; acam ring formed in an annular shape and disposed inside the pump body topermit the cam ring to become eccentric relative to the drive shaft, thecam ring cooperating with the rotor and the vanes to define a pluralityof pump chambers on an inner circumferential side of the cam ring; afirst plate member and a second plate member disposed on axially bothsides of the cam ring; a suction port provided on a side of at least oneof the first plate member and the second plate member and opened to atleast one of the plurality of pump chambers; a discharge port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; asealing member provided on an outer circumferential side of the camring, the sealing member dividing a space on an outer circumferentialsurface of the cam ring into a first fluid pressure chamber and a secondfluid pressure chamber, wherein a flow rate of working fluid dischargedfrom the discharge port is increased when the cam ring moves to thefirst fluid pressure chamber, wherein the flow rate of working fluiddischarged from the discharge port is decreased when the cam ring movesto the second fluid pressure chamber; a metering orifice formed on adischarge passage connected with the discharge port; a pressure controlsection adapted to control a pressure which is introduced into the firstfluid pressure chamber or the second fluid pressure chamber, thepressure control section comprising a high pressure chamber into whichan upstream pressure of the metering orifice is introduced, a mediumpressure chamber into which a downstream pressure of the meteringorifice is introduced, and a low pressure chamber connected with areservoir tank for storing working fluid; a relief valve providedbetween a downstream side of the metering orifice and the reservoirtank, the relief valve being adapted to be opened by receiving apressure greater than or equal to a predetermined level and thereby todrain the downstream pressure of the metering orifice into the reservoirtank; and a variable metering mechanism configured to narrow across-sectional area of opening portion of the metering orifice to alarger extent as the eccentricity of the cam ring becomes smaller whenthe relief valve is open.
 16. The variable displacement vane pump asclaimed in claim 15, wherein the cam ring is adapted to swing so as togradually block the opening portion of the metering orifice, thevariable metering mechanism being achieved by the metering orifice andthe cam ring; and the metering orifice comprises the opening portionformed in an axial end surface of the first plate member or the secondplate member.
 17. The variable displacement vane pump as claimed inclaim 15, wherein the variable metering mechanism is configured togradually narrow the opening portion of the metering orifice after thecam ring has swung to its position having a predetermined angle.
 18. Thevariable displacement vane pump as claimed in claim 15, furthercomprising a pilot orifice provided on a passage connecting thedischarge port with the high pressure chamber.
 19. A variabledisplacement vane pump comprising: a pump body; a drive shaft supportedrotatably by the pump body; a rotor disposed inside the pump body andadapted to be rotatably driven by the drive shaft, the rotor beingformed with a plurality of slots spaced from each other in acircumferential direction of the rotor; a plurality of vanes received bythe slots so as to be movable out from the slots and into the slots; acam ring formed in an annular shape and disposed inside the pump body topermit the cam ring to become eccentric relative to the drive shaft, thecam ring cooperating with the rotor and the vanes to define a pluralityof pump chambers on an inner circumferential side of the cam ring; afirst plate member and a second plate member disposed on axially bothsides of the cam ring; a suction port provided on a side of at least oneof the first plate member and the second plate member and opened to atleast one of the plurality of pump chambers; a discharge port providedon a side of at least one of the first plate member and the second platemember and opened to at least one of the plurality of pump chambers; asealing member provided on an outer circumferential side of the camring, the sealing member dividing a space on an outer circumferentialsurface of the cam ring into a first fluid pressure chamber and a secondfluid pressure chamber, wherein a flow rate of working fluid dischargedfrom the discharge port is increased when the cam ring moves to thefirst fluid pressure chamber, wherein the flow rate of working fluiddischarged from the discharge port is decreased when the cam ring movesto the second fluid pressure chamber; a metering orifice formed on adischarge passage connected with the discharge port; a pressure controlsection adapted to control a pressure which is introduced into the firstfluid pressure chamber or the second fluid pressure chamber, thepressure control section comprising a high pressure chamber into whichan upstream pressure of the metering orifice is introduced, a mediumpressure chamber into which a downstream pressure of the meteringorifice is introduced, and a low pressure chamber connected with areservoir tank for storing working fluid; a fluid-pressure sensoradapted to sense a pressure discharged from the discharge port; a reliefvalve adapted to drain the downstream pressure of the metering orificeto the reservoir tank, and a pressure-using device adapted to use apressure supplied from the discharge port; and a variable meteringmechanism configured to narrow a cross-sectional area of flow passage ofthe metering orifice on the basis of an output signal of thefluid-pressure sensor.
 20. The variable displacement vane pump asclaimed in claim 19, wherein the variable metering mechanism is achievedby an electromagnetic valve adapted to be opened based on the outputsignal of the fluid-pressure sensor.